Channeled shadow mask

ABSTRACT

A shadow mask for colored TV picture tubes contains the conventional foraminous or translucent area formed by multiple vertical rows of miniature apertures or slits with the improvement being a set of parallel elongated channels or grooves which are located between the vertical rows of slits or apertures to produce a self-supporting mask which has a smoothly curved surface.

United States Patent 1 1 Brown CHANNELED SHADOW MASK [75] Inventor:Silas A. Brown, Lake Elmo, Minn.

[73] Assignee: Buckbee-Mears Company, St. Paul,

Minn.

22 Filed: Sept. 20, 1974 211 Appl. No.: 507,689

[52] US. Cl. 313/403; 29/25.14 [51] Int. Cl. H01J 29/07; l-lOlJ 29/08[58] Field of Search 313/403, 402, 407, 404,

[56] References Cited UNITED STATES PATENTS 3,653,900 Black 313/408 XOct. 28, 1975 3,753,663 3/1973 Black 313/402 X Primary Examiner-RobertSegal Attorney, Agent, or FirmJacobson and Johnson [5 7] ABSTRACT Ashadow mask for colored TV picture tubes contains the conventionalforaminous or translucent area formed by multiple vertical rows ofminiature apertures or slits with the improvement being a set ofparallel elongated channels or grooves which are located between thevertical rows of slits or apertures to produce a self-supporting maskwhich has a smoothly curved surface.

7 Claims, 5 Drawing Figures U.S. Patent 0t.2s, 1975 Sheet 1 of23,916,243

CHANNELED SHADOW MASK BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to making a curved shadowmask having small openings or slots for use in colored television tubesas well as for other articles. More specifically, this is an etchingprocess for producinga flat mask which can be bowed or curved to producea curved shadow mask having a smooth, continuous gradual curve.

2. Description of the Prior Art In a colored television picture tube, ashadow mask or aperture mask is located between the electron guns at therear of the tube and phosphor coated face plate at the face of the tube.Electron beams pass through the tiny openings or apertures in the shadowmask and impinge on a suitable color-producing phosphor dot on the faceplate. Located in line with the openings of the shadow mask are threephosphor dots, lines or the like, one dot or line for each of the threeprimary colors. During operation of the picture tube, the shadow maskopenings are used as a guide for the electron beams. In one style ofthese prior art masks the openings are relatively small and elongated.The process of making the openings in an elongated shape is shown anddescribed in the co-pending application of John .I. Frantzen and Lee C.Barton titled Etching Process for Accurately Making Small Holes in ThickMaterials, U.S. Pat. Ser. No. 487,665, filed July 11, 1974. The presentinvention relates to making a mask having elongated openings thereinwhich is to be formed into a continuous rounded surface.

Recently, the shadow mask industry has begun using the types of shadowmasks which have elongated slots or slits in the mask. The minimumdimension of the openings in these masks are usually less than thethickness of the mask material. Furthermore, the openings are usuallylocated in vertical alignment on the mask. All these factors havecoacted to make it difficult to etch a shadow mask and then form themask into a curved mask suitable for use in a television picture. One ofthe problems encountered with these masks is that the mask materialruptures easily when the mask is formed into the required curvedsurface. The present invention has overcome the difficulty in forming asmoothly curved mask from a sheet of flat material by providing a set ofparallel recessed grooves which allow the mask to be formed into acurved shape but do not structurally weaken the mask.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is anenlarged rear sectional view of a portion of a television aperture mask;

FIG. 2 is an enlarged front sectional view showing the channels locatedin the television aperture mask;

FIG. 3 is a sectional end view of a portion ofa televi' sion aperturemask;

FIG. 4 is a sectional view taken along the lines of 44 of FIG. 1; and

FIG. 5 is a pictorial view of a curved mask as it appears in atelevision picture tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring toFIG. 1, referencenumeral 9 generally designates an enlarged section of an etched flatmask which is to be formed and installed in the glass envelope ofatelevision picture tube. Mask 9 contains a plurality of rows ofelongated openings 11 which are located in alignment on the mask. Thewidth of the openings is denoted by reference letter a. Surrounding eachof the openings 1 1 is a recess region 10. Recess region 10 has beenformed in the mask in order that the openings 11 can be accuratelyetched into the mask 9. That is, ifthe minimum dimensions of the openinga are less than the thickness of the mask T (FIG. 3), it has beendifficult if not impossible to directly and accurately etch such smallopenings without using some type of compensation techniques.Consequently,'a cavity or recessed region is first etched into the mask.Next, an opening is etched through the bottom of the cavity. Thus, themask is left with the appearance of cavities or recesses in which thebottom has been removed to provide an opening therethrough. Although themask retains its structural rigidity because of the thickness of themask, when the mask has openings made by the process of removing extramaterial around the opening, it produces regions of low mass betweenregions of high mass that make it difficult to form or bend the maskinto a smoothly rounded mask. Referring to FIG. 4, reference numeral 17denotes a low mass region 17 which is located between the ends of theopenings 10. One of the problems of forming the flat mask into a curvedmask is that the low mass regions which are referred to as tie bars areeasily ruptured or deformed when the mask is subjected to the formingprocess. One of the prior art techniques to eliminate this problem is toremove the tie bars and use a set of parallel filaments. However, thefilaments must be supported in tension in order to maintain properalignment and spacing of the filaments. Still another solution is tomake the mask out of thinner material, however, this tends to destroythe structural rigidity of the mask to a point where it is whollyunacceptable as a self-supporting aperture mask.

The importance of obtaining a smoothly curved aperture mask is that thespacing between the openings must be accurately aligned in order toproduce a television picture of good quality.

Referring to FIGS. 2 and 3, reference numerals l5 and 16 designate a setof parallel elongated channels which are located on each side of opening1 1. Although FIGS. 2 and 3 reveal only two channels, the channels arelocated between all the rows of vertical openings.

Channels 15 and 16 are identical in size and shape and have a widthdesignated by W and an unetched depth designated by reference letter S.The channels are etched in the face of the mask which is opposite theside of the mask containing the recess region 10. It has been found thatby etching a set of parallel continuous channels produces a mask whichcan be formed with a curved surface without rupturing the tie bars ordeforming the surface of the mask.

As can be seen in FIG. 3, the cross section of the mask becomes moreuniform without regions of high mass adjacent to regions of low mass. Itis this feature which is believed to allow the mask to be accurately 3formed into a self-supporting shadow mask.

Referring to FIG. 5, reference numeral 20 designates how a mask mayappear in its formed or bowed shape. That is, the surface of the maskhas a spherical curvature thereto. In order to illustrate the positionof the line of openings 22 and the position of the channels 21, threerows of openings and channels are shown in mask 20. The channels extendparallel to the rows of openings and extend from the top side of themask to the bottom side of the mask. It should be understood that therows of openings and channels extend completely across the face of themask but for purposes of illustration, only three rows of openings andchannels have been shown.

The openings and the thicknesses of a typical mask are pointed out bythe following example.

EXAMPLE A sheet of material having a thickness T of 0.0056 inches wasetched until the cavities had a dimension b of 0.0142 inside, with anopening a of 0.0045. The depth of unetched portion of the opening c was0.0023 inches. The channels which run parallel to the rows of elongatedopenings had an etched width W of 0.0ll inches and an unetched depth Sof 0.0017 inches. The mask was formed into a curved shadow mask withoutany rupturing of the tie bars occurring during the forming process.

From the above example and test work performed on the present invention,it has been found that the present invention has its greatest utilitywhere the mask thickness exceeds the minimum dimension of the opening inthe mask. [t is these particular masks which are extremely difficult toform into a properly curved surface without rupturing the tie barsbetween the openings.

I claim:

1. An aperture mask having a plurality of openings therein for theprojection of an electron beam therethrough comprising:

a sheet of metal having a topside and a bottomside,

said sheet of metal having an aperture region defined by a plurality ofopenings therein, said plurality of openings comprising a plurality ofrows of openings located in substantial alignment to thereby form aplurality of spaced rows of openings, each of said plurality of openingshaving a cavity surrounding the opening in said mask;

a plurality of channels substantially symmetrically located between therows of said openings and extending from the topside of said mask to thebottomside of said mask with at least one channel located betweenadjacent rows of openings; said plurality of channels and cavitieshaving related depths to effect uniformity of mask shaping withoutrupturing of the mask material.

2. The mask of claim 1 wherein said sheet of metal having openingstherein are elongated.

3. The mask of claim 2 wherein said plurality of channels are located onthe one side of said mask and the cavities are located on the oppositeside of the mask.

4. The mask of claim 3 wherein the openings have a minimum dimensionless than the thickness t of said mask.

5. The mask of claim 4 wherein the plurality of channels are spacedequidistant between the rows of said openings.

6. The mask of claim 5 wherein the plurality of channels have an etcheddepth which is at least half the thickness t of said mask.

7. The mask of claim 6 wherein the mask has a cross sectional area whichis characterized by substantially uniform thickness.

1. An aperture mask having a plurality of openings therein for theprojection of an electron beam therethrough comprising: a sheet of metalhaving a topside and a bottomside, said sheet of metal having anaperture region defined by a plurality of openings therein, saidplurality of openings comprising a plurality of rows of openings locatedin substantial alignment to thereby form a plurality of spaced rows ofopenings, each of said plurality of openings having a cavity surroundingthe opening in said mask; a plurality of channels substantiallysymmetrically located between the rows of said openings and extendingfrom the topside of said mask to the bottomside of said mask with atleast one channel located between adjacent rows of openings; saidplurality of channels and cavities having related depths to effectuniformity of mask shaping without rupturing of the mask material. 2.The mask of claim 1 wherein said sheet of metal having openings thereinare elongated.
 3. The mask of claim 2 wherein said plurality of channelsare located on the one side of said mask and the cavities are located onthe opposite side of the mask.
 4. The mask of claim 3 wherein theopenings have a minimum dimension less than the thickness t of saidmask.
 5. The mask of claim 4 wherein the plurality of channels arespaced equidistant between the rows of said openings.
 6. The mask ofclaim 5 wherein the plurality of channels have an etched depth which isat least half the thickness t of said mask.
 7. The mask of claim 6wherein the mask has a cross sectional area which is characterized bysubstantially uniform thickness.